This invention relates generally to watercraft and more specifically to control systems and motors for watercraft that use electric motors and/or electric control systems.
Electric boats once dominated the power watercraft field but became disfavored due to the lower power to weight ratio and lower speed available in electric boats compared to fossil burning watercraft that later developed. Public interest in electric watercraft has resurfaced recently due to their advantages of lower pollution, lower noise, and in some cases elegance, compared with air breathing fossil fueled watercraft. Because of their use of low energy density power supplies such as lead acid batteries, metal hydride batteries, and in the future, fuel cells (including the chemical energy conversion unit) and the like however, electric boats have limited range and speed compared to equivalent sized fossil boats. Accordingly, any improvement in propulsion efficiency of an electric boat would directly ameliorate this problem and improve acceptance of electric boats by the public.
Much electric boat motor and battery technology arose from advances in the electric golf cart and electric car industries. Accordingly, most commercial motors used in electric boats have been designed for those other uses. Many of those active in the electric boat industry use series wound motors and believe that the torque versus speed characteristics of this motor are well optimized for electric boating because the motor speed automatically increases to reach a suitable maximum propeller resistance (Paul Kydd, Electric Boat Journal Issue 4, Vol. 6). On the other hand, electronic technologies designed for golf carts, cars and trolleys, such as electrified rails that provide electric power, satellite/roadway navigational aids, automated braking systems, back up radar monitor systems and the like have limited or no use in electric boats. Thus, the electric boat industry cannot rely on aftermarket parts and solutions from these other industries but must invest in and exploit new technologies that solve the particular problems of electric boats.
Improved batteries and motors are the automotive technology advances that seems to relate most to electric boating. Recent developments in permanent magnet direct current motors that utilize high powered rare earth magnets, as exemplified by the Lynch motor taught in U.S. Pat. No. 4,823,039 are greatly welcomed. Such motors are expected to bring great improvements to the industry. However, most motors still are limited to having optimum performance peaks at a narrow or limited range of speed and load. Moreover, even the best motors, which utilize rare earth element high powered permanent magnets generally have low efficiencies at low speed.
A review of advances in the electric motor field would not be complete without acknowledging the improvements made by David Tether, including, among other things, permanent magnet motors having planetary/sun gear arrangements that provide significant advantages for regeneration and for use in watercraft, especially sailboats, as represented in U.S. Pat. Nos. 5,575,730, 5,067,932, 5,851,162 and 5,863,228. Also, the xe2x80x9cecyclexe2x80x9d motor (see www.ecycle.com) promoted and refined by Daniel J. Sodomsky, which has many desirable attributes, with high performance magnets in the rotor and generally high performance overall. These motors alleviate many problems but still, like other motors before them, generally have highest efficiency at a high rotational speed. Thus, a general problem with applying electric motors in watercraft is that motor efficiency drops off at low speed and propulsion efficiency drops off at high speed. The relative lack of discussion of these phenomenon reflects the fact that most motors designers take the problems for granted. It should be noted in this context that shunt wound motors sold in watercraft from the Electric Launch Company of Highlands, New York seem to be controlled by a circuit that independently drives the two coils. However, details of the algorithm used have been kept from the public and the control circuit is sold in a permanent opaque block of epoxy, and details of the circuit appear not to have been published.
Another problem in the watercraft industry that appears to have been overlooked generally in the electric boat field is the need to match propeller slip with boat output at different watercraft velocities. Typically, a fixed propeller of a watercraft is chosen based on optimum performance of a given motor and boat at high speed or at low speed, or a compromise between the two speeds. During use, the operator merely increases power to the motor without regard to propeller slippage until the watercraft reaches a desired speed. This strategy may suit the operation of boats that have a maximum speed of only a few knots and may be appropriate for fossil burning watercraft in an era of very cheap energy. However, high speed personal watercraft, particularly heavy ones that can travel fast may require time to reach high speeds, and excessive propeller slip becomes more of a problem that noticeably affects efficiency of battery use, fuel cell power use and hydrocarbon combustion use in fossil fueled watercraft. Furthermore, the very high propeller slippage condition of cavitation becomes greater as higher revving motors are used to achieve higher speeds. These problems generally have remained unrecognized because the commercial electric boat industry (in particular, pleasure craft less than 35 feet long) focuses on slow boats limited to their displacement hull speeds.
Yet another problem with many electric motors used for watercraft is the mechanism used for removing excess heat. In many terrestrial applications an electric motor is air cooled. In boats, however, the moist and often salty marine environment is inhospitable to many materials used. Special materials and finishes may be required. A particular problem in this regard is when the entire motor is sealed. Trolling motors have been designed that rely on transfer of heat from an exterior case that surrounds the motor, with water. Such motors are generally thought as not very reliable for long term use. In some cases, an enclosed motor case cannot completely contact water, and heat build up is a greater concern. An example of the latter is the motor configuration used by Maruta Electric Boatworks LLC, (www.aquaskate.com) wherein an electric motor is completely enclosed within a sealed hull. As trolling motors become more widely used for a variety of new boat hull designs that limit contact of water with the motor case, removal of heat will become more of a problem. Use of a separate pump with its own electrical circuit and pipes adds an extra level of complexity which undesirably increases costs and presents further opportunity for breakdown. A passive system or simpler system would advance this art.
Yet another problem is that control systems such as auto pilots have been developed primarily for complex operation in larger vessels, where high cost systems have been first adopted and operators are accustomed to training. Simple one button or twist knob analog operation of simple controls such as auto heading is desired by many pleasure boaters who may not want to read an operation manual before using a control.
In sum, boats are very sensitive to propulsion efficiency but most of the motors and their control systems for electric boats have been developed for the automobile and golf industries. Further, present commercial electric pleasure craft are designed primarily for low speed operation and manufacturers have not seriously challenged the limits of motor performance. Any motor or control system that improves the overall efficiency and convenience of pushing a boat would yield rich dividends in extending the performance of the power supply and in gaining further public acceptance of products from this industry, particularly for electric motor powered pleasure watercraft less than 45 feet long.
During his design studies and construction of practical working examples of electric boats the inventor has made a number of discoveries that directly lead to improved propulsion efficiency and convenience, particularly at low speed. During this work, control systems also were discovered that provide improved propeller safety. These and other advantages of the invention will be appreciated by a reading of the specification.
One embodiment of the invention is an electronic motor control that alters the motor speed/torque output at varying boat speed to more closely match the increasing torque requirements of an attached propeller at increasing boat speeds. One such embodiment of a brushed motor is carried out by altering the armature voltage to change speed, while altering the magnetic field (fixed coil) around the armature, using at least two different magnetic field strengths on the fixed coil, with higher magnetic field(s) at lower rpm and lower field(s) at higher rpm. In a related embodiment, the magnetic field surrounding the armature is altered to at least three values of increasing magnetic strength with increasing rpm. In yet another embodiment the magnetic field is altered to at least 4 values. In yet another embodiment the magnetic field is altered with an algorithm or look up table to determine an increasing magnetic field for a higher rpm range to provide a smoother transition through more than 4 magnetic field strength values.
In yet another embodiment a permanent magnet magnetic field is modified by a superimposed electromagnetic field that optionally may increase the combined field at higher rpm to achieve higher torque and that may be reversed and subtracted from the field at lower rpm to achieve better lower speed efficiency. In yet another embodiment a permanent magnet magnetic field is modified by a superimposed electromagnetic field obtained by two separate electromagnets, which preferably comprise at least one inner electromagnet and an outer electromagnet. At higher torque (greater rpm) the inner magnet is progressively excited and at lower torque at lesser rpm the outer magnet is progressively excited more. In another embodiment the distance between the rotor and stator (or field and rotor) is adjusted to modify the magnetic field(s). In another embodiment the reluctance of the magnetic path between stator and rotor is modified for less magnetic field strength at lower rpm.
Another embodiment is an electronic control method for enhancing the efficiency of electric motor driven propeller watercraft comprising detecting the speed of the watercraft directly or indirectly, detecting the rotational speed of the electric motor, comparing the result of step (a) with the result of step (b) to estimate an expected propeller slip, and adjusting power to the motor to achieve a desired propeller slip. In other related embodiments, the first step is carried out by a procedure selected from the group consisting of detecting a signal or difference from a GSA receiver; detecting a signal or signal difference from a speedometer; and inputting a value from by a computer that monitors one or more electrical variables of the motor such as power, voltage or trip running time; the second step may be carried out by a procedure selected from the group consisting of detecting the motor rotational speed; indirectly determining the motor speed by detecting the current in the motor armature, the voltage of the motor armature, the impedance of the motor armature, the current in the motor field winding, the voltage of the motor field winding, and/or the impedance of the motor field winding; and detecting the propeller speed via magnetic or optical sensing. In related embodiments the desired propeller slip is less than 50%, and the rotational speed of the electric motor is determined by sensing the voltage of the motor power. In another embodiment the motor is adjusted to provide lower slip with faster boat and propeller speeds.
Another embodiment of the invention is an electronic control for enhancing the efficiency of electric motor driven watercraft a having a propeller over a range of speeds comprising a propeller rotation speed signal, a motor power controller, and a comparator for monitoring the propeller rotation speed signal, wherein the controller increases power to the motor by an increment and waits while the comparator detects when the propeller speed signal has reached a steady state or near steady state level, after which the controller increases power again. In further embodiments the propeller rotation speed signal is motor drive voltage, and the comparator repeats incremental increases until a desired endpoint power is reached.
Another embodiment of the invention is an electronic control for enhancing the efficiency of electric motor driven watercraft a having a propeller over a range of speeds comprising a motor power signal, a motor voltage controller; and a comparator for monitoring the motor power signal, wherein the controller increases voltage to the motor by an increment and waits while the comparator detects when the motor power has reached a higher steady state or near steady state level, after which the controller increases voltage again. In related embodiments the motor power signal is motor current, and the comparator repeats incremental increases until a desired endpoint motor voltage is reached.
Another embodiment is an electronic control device that controls propeller slip of an electric motor powered watercraft, comprising a detector of propeller speed, a detector of the watercraft""s speed, and a circuit that controls power to the armature of the motor, a field winding of the motor or both, wherein a signal from the detector actuates the circuit to adjust propeller slip according to a predetermined relationship between propeller and boat speed. In related embodiments the detector is selected from the group consisting of a motor speed detector, voltage input to the motor, an optic or magnetic sensor of propeller speed and a computer that monitors power and time to estimate approximate speed; a watercraft contains such electronic control devices; the circuit decreases power to the motor when the propeller speed exceeds a predetermined limit for a given boat speed; the predetermined relationship between propeller and boat speed may be a single value for all boat speeds; and the electronic control device further comprises at least a second control condition that increases the allowable propeller slip to provide higher slippage for greater acceleration.
Another embodiment of the invention is a non-mechanical electronic control system for inhibiting cavitation of a propeller driven electric powered watercraft, comprising a boat speed monitor, and a control circuit, wherein the control circuit monitors motor voltage as an index of propeller speed and decreases motor power when the motor voltage is too high for a given boat speed. In related embodiments the control circuit contains a microprocessor look up table of motor voltage versus boat speed values for use in determining when to lower motor power; and the control circuit further comprises a first electronic comparator circuit or software subroutine that compares the motor voltage with boat speed and a second comparator circuit or software subroutine that compares the results of the first electronic comparator circuit or software subroutine with a reference value and outputs a motor power decrease signal when the comparison shows that the reference value has been surpassed.
Another embodiment of the invention is a simplified heading cruise control for a watercraft, comprising one or more ratiometric output geomagnetic sensors mounted to the watercraft and that output one or more analog signals that correspond to geomagnetic heading, a circuit that analyses the signal(s) from the one or more geomagnetic sensor(s) to output one or more correction signals for altering course, and a maximum of one on/off switch on the watercraft dash required for activating the cruise control. In related embodiments the simplified cruise control further comprises a propeller speed or boat speed signal that automatically turns on the heading cruise control upon exceeding a set speed to allow automatic heading correction at higher cruise speeds; a switch mounted on at least the motor throttle or steering wheel control, wherein activation of the switch turns the heading cruise control on or off; the switch mounted on the motor throttle or steering wheel control is a body capacitive switch that is activated upon electrical contact between skin of the watercraft operator and the throttle or steering control; and further comprises a rotating knob for directly setting a desired course, wherein the one or more ratiometric output geomagnetic sensors are attached to the rotating knob and rotate with the knob.